Liquid communication between a ground formation and a wellbore is often established or enhanced by perforation tunnels in the formation. The perforation tunnels are created at the location of the formation, and they typically extend perpendicularly into the formation. Perforation tunnels are traditionally made using shaped charges of chemical explosives that inject a material into the formation, creating the tunnel.
In conventional perforating, the explosive nature of the process shatters sand grains of the formation. A layer of “shock damaged region” having a permeability lower than that of the virgin formation matrix may be formed around each perforation tunnel. The process may also generate a tunnel full of rock debris mixed in with the perforator charge debris. The shock damaged region and loose debris in the perforation tunnels are known to impair the productivity of production wells, or the injectivity of injector wells, and hence negatively impact upon the flow of liquids between the formation and the well.
U.S. Pat. No. 9,057,232 discloses methods and apparatuses for enhancing the oil recovery in oil wells by using shock waves for stimulating an oil-producing formation. This stimulation is inter alia done by creating arbitrary cracks in the formation adjacent previously formed perforation tunnels. The technology according to U.S. Pat. No. 9,057,232 is described used in preparation for hydraulic fracking operations and also during hydraulic fracking operations.